New boiler and stat but room cool need advice please

2wd · 28 Nov 2018

Just had a new vaillant ecotec 28 combi boiler and Honeywell cm727 room stat fitted

We set the temp to 21 degrees and the room heats up nice and warm.

However once it's reached temperature the room starts to cool down to a point where it starts to feel chilly, yet the stat says 21 degrees and the only way we can start to feel warm again is to turn the temp up a degree or 2, then it heats up but we then go through same scenario.

Also when it's reached the set temperature the little flame is always on the stat, even though the boiler isn't firing.

Heating engineer has replaced the stat but still the same.

I thought a digital room stat would keep the temperature at a constant temperature which has been set not heat up then cool down.

To add the stat is in the living room and the rad has no TRV fitted, I have also tried various locations in the living room for the stat.

Appreciate any help or feedback

stem · 28 Nov 2018

It could be that when the radiators are hot, you are feeling the radiant heat from them and when they go off that disappears so you feel cooler even though the room temperature is still the same. To illustrate; you are sitting near a window and the sun appears from behind a cloud and shines on you. Immediately you feel warmer but the room temperature won't have changed you are just feeling the radiant heat from the sun. A few seconds later the sun disappears again and you feel cooler, but again the room temperature won't have changed.

Is the stat located in a position where it is getting warmed by something else? I once was called to check a thermostat that was located in a hall, in the room immediately behind it was a fridge, the back of which was warm because of the motor and compressor. It also warmed the wall behind the thermostat and made the thermostat read 2 degrees higher that the room temperature actually was. Moving the thermostat to the opposite wall solved it.

Or is the stat tucked in a warm part of the room but you are sitting near a window, air vent or other source of cool air that cools more quickly?

Is should be pretty easy to get a digital thermometer and check the actual temperature in the room to see if the temperature is dropping or not.

The bit that puzzles me a bit is that you say that turning the thermostat up repeats the scenario. Do you mean that for example that if you were to set the thermostat to 23 degrees when the heating goes off, you start to feel chilly before it comes on again?

2wd · 28 Nov 2018

Hi Stem thanks for the quick reply
I understand what you mean about radiated heat and is something I have considered but when it cools down the room feels really chilly.
The stat isn't being influenced by anything and I have tried about 6 locations in the living room to make sure.
Yes when I up the temperature the same happens again, warms up nicely to the set temp then knocks off and cools down to chilly.
My understanding of temperature is for example if it's 21 degrees it's 21 degrees not 21 degrees but feels like 16.
Edit
It's a bungalow with a fully insulated loft and cavity wall insulation and just had new double glazed windows with that fancy heat refecting glass, so the heat isn't easily escaping anywhere

ianmcd · 29 Nov 2018

if the flame icon is showing as on at the room stat but the boiler is off ,you need to turn the boiler thermostat up , it is over ridding the room thermostat

2wd · 29 Nov 2018

Boiler thermostat is set to 75

Mottie · 29 Nov 2018

This might not ne relevant but on my recently fitted Vaillant Ecotec 18kw, from a cold start it works at maximum temp on the boiler - it shows max bars on the digital display etc. I piddled about with the settings and set it to 15kw but from a cold start, I only got just over 2/3 of the bars up and it was taking a lot longer to get the rads hot so I put it back to 18kw. The temp is set to 65 degrees and that is a different setting to the kw output if that makes sense. Maybe your boiler max kw output isn't set high enough? On the other hand, I could be talking total ****** but that's nothing new for me!

ianmcd · 29 Nov 2018

should be fine at that then, check the boiler display when you start to feel cold and see if the boiler still registers a demand for heat while the stat is still showing a demand if it does the fault is not with the thermostat, your boiler has a setting called anti-cycle which means that once the heating is satisfied , it wont come back on for a set period, to save false cycling, your boiler comes factory set at 20 mins which might be a bit too long for your needs, this can be adjusted though

2wd · 29 Nov 2018

Thanks ianmcd
That 20 minutes may be the answer

Grumpy Gasman · 29 Nov 2018

Appliance configuration d.00 will be factory set to ‘auto’, remove ‘auto’ and adapt heat load to a suitable KW rating.

stem · 29 Nov 2018

If the boiler was set for a 20 minute delay would the below happen though?

2wd said:
the only way we can start to feel warm again is to turn the temp up a degree or 2, then it heats up but we then go through same scenario.

It would have to be pretty coincidental that every time the stat was adjusted coincided with the exact ending of the 20 minutes.

2wd · 29 Nov 2018

I have the stat set to 21 degrees
I'm going to experiment and have it set to 23 I'm also having a hive installed on Friday to replace the Honeywell CM727
Only because they had a really good black Friday deal including a free echo for

I'll see what happens

ianmcd · 29 Nov 2018

the hive cant over rule the boiler seetings , if fitting a hive set you delay to 0 and let the hive do its work

2wd · 29 Nov 2018

ianmcd said:
the hive cant over rule the boiler seetings , if fitting a hive set you delay to 0 and let the hive do its work

Ok cheers
I'll speak with the installation guy tommorrow

D_Hailsham · 30 Nov 2018

ianmcd said:
if the flame icon is showing as on at the room stat but the boiler is off ,you need to turn the boiler thermostat up , it is over ridding the room thermostat

That's not correct. The flame icon shows all the time there is a demand for heat but the TPI logic in the CM727 could be in an "off" phase.

Honeywell's explanation is:

The relay box cycles the relay on and off for times proportional to the demand signal (0-100%) from the room thermostat. The [flame] symbol only indicates that the demand value is greater than 0%.

If you lower the target temperature 1 to 1.5 degrees below the actual room temperature the flame will disappear as the demand is now zero.

I'm not convinced that the apparent drop in temperature is anything to do with the CM727 as I have had a CM927 for over 10 years and have never experienced the problem. It keeps the house rock steady at 21C all day long.

2wd · 30 Nov 2018

Hi D Hailsham

Thanks for that
In that case wouid you think reducing the anti cycling time would help me

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New boiler and stat but room cool need advice please

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